Click here to listen to the full program, which first aired June 13, 2017 at 6:30 p.m.

Summer is upon us and that means more of the bugs that made international headlines last year – mosquitos. What progress has been made in the fight against the Zika virus? Can we cure Zika, or prevent it? And what can residents do to help?

Zika is a scary virus because of the terrible birth defects it can cause. Now scientists have a clearer sense of the size of that risk.

The U.S. Centers for Disease Control and Prevention identified 2,549 pregnant women with the Zika virus in Puerto Rico and other U.S. territories between Jan. 1, 2016 and April 25, 2017. The CDC found that 122 of these women — about 5 percent — gave birth to babies with birth defects such as small heads (known as microcephaly).

A series of medical images published Tuesday offer the most complete picture, so far, of how the Zika virus can damage the brain of a fetus.

"The images show the worst brain infections that doctors will ever see," says Dr. Deborah Levine, at Beth Israel Deaconess Medical Center in Boston, who contributed to the study. "Zika is such a severe infection [in fetuses]. Most doctors will have never seen brains like this before."

Mosquitoes may be one of summer’s nuisances. But the ones carrying Zika, a virus that has spread through Latin America and could be transmitted in the United States this summer, are triggering public health warnings — especially among women of childbearing age — because of Zika’s propensity to cause birth defects.

As the international epidemic of Zika virus disease has unfolded and led to devastating birth defects for at least 1,300 children in eight countries, an agonizing question has persisted: What is the chance that an infected pregnant woman will have a baby with these defects?

As scientists struggle to understand the threat posed by Zika virus, there's another viral infection that's a known danger in pregnancy and that harms 100,000 babies a year, even though it has been preventable with a vaccine since 1969.

The disease is rubella, or German measles. Like Zika, the rubella virus often causes either a mild rash or no symptoms at all.